Device for preparing multi-component metal hydroxide

The present invention relates to a device for preparing multi-component metal hydroxides, a method for preparing multi-component metal hydroxides using the same, and metal precursor powders prepared using the same.

Lithium secondary batteries are mainly used for digital devices such as laptops and mobile phones and lithium secondary batteries are finding ever expanding applications from portable information and communication devices to electric vehicles, hybrid automobiles, aerospace, and energy storage systems (ESS) based on cost reduction and performance stabilization through mass production and technological development and the market for lithium secondary batteries is expected to continue to grow.

The core materials of lithium secondary batteries are a cathode active material, an anode active material, an electrolyte, and a separator. Thereamong, the cathode active material is the most core material for manufacturing secondary batteries and is divided into lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium iron phosphate (LFP), and the like, depending on constituent materials thereof.

Recently, there is an increasing demand for high-capacity and high-density cathode active materials to improve the performance of lithium secondary batteries. For this purpose, an active material that has an improved mixture density by blending a plurality of different types of cathode active materials in, for example, a bimodal or trimodal form is suggested.

However, a plurality of types of active materials having different particle sizes should be separately calcined and then mixed in order to prepare the blended cathode active material. Therefore, there are problems in that the process cost increases and productivity decreases compared to the cost.

Accordingly, a co-sintering method in which a plurality of types of precursors are mixed in a specific ratio in a precursor step and simultaneously fired, instead of blending the cathode active materials, has been proposed. In such a method, it is important to satisfy the requirements to make the diffusion of Li constant by controlling the powder properties of the precursor particles for each size. Thereamong, controlling the distribution of the precursor is one of the most important factors.

As described above, control of the properties of the precursor is an important factor in order to improve the properties of the cathode active material. Since the properties of cathode active materials strongly reflect the properties of the precursor, the precursor may require properties similar to those of the cathode active material.

Meanwhile, representative methods for preparing precursors include a method based on a continuous stirred-tank reactor (CSTR), which simultaneously performs feeding and co-precipitation of raw materials and discharge of precursors formed as particles, and a batch-type method in which raw materials are fed and reacted in a predetermined volume of the reactor for a given period of time and precursors are discharged after completion of the reaction.

The CSTR-based method has advantages in that it is easy to control the metal composition ratio and the mixture density is excellent due to wide particle distribution in terms of energy density. Since feed of raw materials and discharge of products are continuously performed at the same time, there may be differences in residence time and reaction time in the reactor between the precursors generated in the reactor. This may cause a problem in that even the size and composition of the generated particles are non-uniform.

In addition, when the reaction time is excessively long, the degree of completeness of the secondary particles increases and the amount of fines detached from the secondary particles increases. On the other hand, when the reaction time is excessively short, the degree of completeness of the primary particles decreases and the degree of formation from the primary particles to the secondary particles decreases, thus disadvantageously causing an increase in the amount of fines and decreases in sphericity and density.

As described above, the CSTR-based precursor preparation method exhibits excellent energy density due to high mixture density thereof, but has several problems such as deterioration of electrochemical properties due to the different thermodynamic energies of Li diffusion depending on the size of particles during firing. Therefore, in recent years, there is a tendency to adopt a batch-type method for preparing a precursor that is capable of easily controlling the particle size (particle diameter) and is advantageous in preparing a precursor having a uniform particle size.

However, the batch-type precursor preparation method has various problems. More specifically, since raw materials should be continuously fed and stirred in order to form or grow precursors in a batch-type reactor, in order to form small metal particles (crystal nuclei) and grow the metal particles, the raw materials should be continuously fed. In this process, a problem may occur that the reactor is saturated before metal particles grow to target levels (size, shape, density and the like).

When the reactor is saturated, the feed of raw materials to grow metal particles should be stopped to terminate the reaction, or a part of the intermediate reactant should be discharged from the reactor to secure an area where raw materials are fed. The discharged intermediate reactant should be used for other applications or discarded, which may lead to problems with reduced productivity.

In the batch-type co-precipitation process, the volume of the reactor may be increased to prevent saturation of the reactor. However, this may make it difficult to secure uniformity of the precursor and obtain an improvement in process efficiency due to the deteriorated production efficiency compared to the volume of the equipment.

Accordingly, there is an increasing need for a novel technology capable of solving these problems.

Therefore, the present invention has been made to solve the above and other technical problems that have yet to be solved.

Specifically, it is an object of the present invention to provide multi-component metal hydroxide that has a particle distribution controlled to a desired level while solving the problems of conventional general batch-type or CSTR-type co-precipitation processes by easily controlling particle distribution and BET of metal particles (multi-component metal hydroxide) included in the multi-component metal slurry using a preparation device having a novel configuration based on a combination of batch-type co-precipitation with reaction solution circulation.

In accordance with an aspect of the present invention, provided is a device for preparing multi-component metal hydroxide including a raw material feeder for feeding raw materials including a metal raw material, a pH adjuster and a complexing agent, a reactor for reacting the raw materials fed from the raw material feeder to prepare a reaction solution and grow particles of the multi-component metal hydroxide contained in the reaction solution, a storage tank for storing the reaction solution transferred from the reactor, a first duct for transferring the raw materials from the raw material feeder to the reactor, a second duct for transferring the reaction solution from the reactor to the storage tank, a third duct for transferring the reaction solution from the storage tank to the reactor, and an operation controller for controlling operations of the reactor and the storage tank to circulate the reaction solution between the reactor and the storage tank until the particles of the multi-component metal hydroxide grow to a target particle size.

Such a preparation device is a device for preparing multi-component metal hydroxide based on a novel configuration that did not exist in the prior art. This preparation device is capable of preparing multi-component metal hydroxides to desired levels by easily controlling particle distribution, BET and the like without causing a decrease in productivity by circulating the reaction solution between the reactor and the storage tank until predetermined requirements are satisfied.

Among the “raw materials”, the term “metal raw material” may be an oxide, hydroxide or salt containing an alkali metal, alkaline earth metal, transition metal, post-transition metal, metalloid, or non-metal, or a combination thereof. An aqueous solution in which the metal raw material is dissolved or dispersed in a solvent may be provided. As a non-limiting example, the metal raw material may include at least one of nickel, cobalt, or manganese.

The “pH adjuster” controls the pH of the reaction solution produced by the feed of the raw materials to control the formation or growth of particles of the multi-component metal hydroxide in the reaction solution. Any substance may be used as the pH adjuster so long as it is capable of performing this function. As a non-limiting example, the pH adjuster may include at least one of sodium hydroxide, potassium hydroxide or sodium carbonate.

For example, the multi-component metal hydroxide particles may be formed by adjusting the reaction solution to a basic pH atmosphere using the pH adjuster and the multi-component metal hydroxide particles may be set to grow in a lower pH atmosphere. In the process of circulation of the reaction solution between the reactor and the storage tank, the pH atmosphere may be set to be equal to or lower than that in the particle growth conditions.

The “complexing agent” controls the rate of crystal growth by controlling the reaction rate of the reaction solution. Any substance may be used as the complexing agent so long as it is capable of performing this function. As a non-limiting example, the complexing agent may include at least one of ammonium hydroxide, ammonium nitrate or ammonium sulfate.

In one specific embodiment, the operation controller may control the operation of the raw material feeder to continuously feed the raw materials to the reactor until the particles of the multi-component metal hydroxide contained in the reaction solution grow to a target particle size.

Here, there is no particular limitation as to the configuration and shape of the operation controller so long as it is capable of controlling the operation of the device for preparing multi-component metal hydroxide according to the present invention, such as circulating the reaction solution, by controlling the operation of the reactor and the storage tank. As a non-limiting example, the operation controller may be a control system based on a computer system, and manual or semi-manual control by a device operator may also fall within the scope of the operation controller.

The target particle diameter of the particles may vary depending on the intended application, for example, depending on the type and application of the cathode active material to be finally synthesized using the multi-component metal hydroxide prepared in the device of the present invention.

In one specific embodiment, the operation controller may control the operation of the reactor to start transferring the reaction solution from the reactor to the storage tank when at least one of the following requirements is satisfied:

In the above requirement (i), the reaction solution containing the multi-component metal hydroxide in which the particle size or shape, density, or the like does not reach the target level may be considered a kind of “intermediate reactant” and the reaction solution as such an intermediate reactant continuously circulates between the reactor and the storage tank.

For example, in the requirement (ii), when raw materials are continuously fed to the reactor to form and grow particles of the multi-component metal hydroxide, the water level in the reactor rises and when the water level rises to a specific height in the reactor or the filling rate of the reaction solution becomes higher than a predetermined level, if the reaction solution starts to be transferred to the storage tank, saturation of the reactor before the multi-component metal hydroxide grows to a target value (size, shape, density, and the like) can be prevented.

As the reaction solution is transferred to the storage tank in this way, for example, when 5% or more of the internal capacity of the storage tank is filled with the reaction solution, the operation controller controls operation of the storage tank to start retransferring the reaction solution from the storage tank to the reactor. A portion of the reaction solution as the intermediate reactant transferred to the storage tank is re-transferred to the reactor, and the circulation of the reaction solution as the intermediate reactant between the reactor and the storage tank continues to grow particles of multi-component metal hydroxides.

The circulation of the reaction solution as the intermediate reactant between the reactor and the storage tank may continue until the multi-component metal hydroxide grows to a target level (size, shape, density, or the like). When the multi-component metal hydroxide in the reactor and the storage tank grows to the target level, the reaction and circulation are terminated, and the final product, that is, the reaction solution containing the multi-component metal hydroxide grown to the target level may be discharged from the reactor and the storage tank. In addition, since the multi-component metal hydroxide has grown to a target level, there is no need to feed raw materials into the reactor.

Therefore, as a specific example, the operation controller may be set to stop the circulation of the reaction solution and the feed of the raw materials from the raw material feeder when the particles of the multi-component metal hydroxide contained in the reaction solution of the reactor and the storage tank grow to a target particle size or more.

When the circulation of the reaction solution between the reactor and the storage tank is stopped, the particle properties of the multi-component metal hydroxide contained in the reaction solution in the reactor may be identical or similar to those in the storage tank. For example, particles of the multi-component metal hydroxide in the reaction solution in the reactor and the storage tank may have the same average particle diameter or may have an average particle diameter deviation of 1% or less.

In some cases, when the multi-component metal hydroxide contained in the reaction solution in at least one of the reactor or the storage tank grows to a target particle size or more, the operation controller may be set to selectively discharge the reaction solution from the reactor and/or the storage tank.

In this case, the device according to the present invention may further include a collector for receiving the reaction solution discharged from at least one of the reactor or the storage tank.

In at least one of the reactor or the storage tank, for example, a stirrer for stirring the reaction solution filled therein is further provided, so that the overall uniformity of the reaction solution may be further increased.

In one specific embodiment, the third duct may be further equipped with a solid-liquid separator for concentrating the reaction solution transferred from the storage tank to the reactor and the solid-liquid separator may function to increase the concentration of the multi-component metal hydroxide contained in the reaction solution by removing a part of the filtrate of the reaction solution transferred from the storage tank to the reactor.

The circulation of the reaction solution between the reactor and the storage tank may be realized in various ways. For example, the second duct connects the reactor to the storage tank such that a step (height difference) is formed between the reactor and the storage tank. As a result, the reaction solution of the reactor is transferred to the storage tank via the second duct based on the potential energy caused by the height difference. A circulation pump to provide a driving force for re-transferring the reaction solution stored in the storage tank to the reactor may be provided in the third duct.

In this configuration, in connection with the transfer of the reaction solution from the reactor to the storage tank and the re-transfer of the reaction solution from the storage tank to the reactor, an on-off valve may be installed on the second duct and the third duct, respectively, to enable transfer and re-transfer to be determined by the operation controller and thereby control the flow rate, pressure, or the like during transfer and re-transfer.

In one specific embodiment, the device may further include an inert gas feeder for feeding inert gas to at least one of the reactor or the storage tank to reduce the generation of by-products and the possibility of inducing side reactions by maintaining an inert atmosphere. In some cases, the temperature of the reactor and the storage tank may be kept constant by the inert gas.

An example of the preparation device described above is shown in the schematic diagram of. That is, the preparation deviceaccording to an embodiment of the present invention includes a raw material feeder, a reactor, a storage tank, an operation controller, a solid-liquid separator, and a circulation pumpand the like, and further includes a first ductfor connecting the raw material feederto the reactor, a second ductand a third ductfor connecting the reactorto the storage tank. The configuration and operation mechanism thereof have been described above.

The present invention also provides a method for preparing a multi-component metal hydroxide using the device, the method including (a) feeding raw materials from the raw material feeder to the reactor via the first duct, (b) preparing a reaction solution by reaction of the raw materials in the reactor and growing multi-component metal hydroxide particles contained in the reaction solution, (c) transferring a part of the reaction solution from the reactor to the storage tank under predetermined conditions, (d) retransferring a part of the reaction solution from the storage tank to the reactor under predetermined conditions, (e) repeating the above steps (c) and (d) to circulate the reaction solution between the reactor and the storage tank until multi-component metal hydroxide particles grow to a target particle size, and (f) stopping the feed of the raw materials and the circulation of the reaction solution and discharging the reaction solution from the reactor and the storage tank when the multi-component metal hydroxide particles grow beyond the target particle size.

The recirculation of the reactant including transfer and re-transfer conditions has been described in connection with the device above and thus a description thereof will be omitted.

Also, the present invention provides metal precursor powders for preparing a cathode active material for a lithium secondary battery, prepared using the method described above, wherein the metal precursor powders have a particle size standard deviation of 10% or less, preferably 5% or less, more preferably 3% or less.

Other configurations and preparation methods of the cathode active material are known in the art and thus a detailed description thereof will be omitted herein.

As described above, advantageously, the device for preparing multi-component metal hydroxides according to the present invention provides multi-component metal hydroxide having target properties because it is capable of easily controlling particle distribution and BET of the multi-component metal hydroxide, and significantly reduces a decrease in productivity in the preparation of multi-component metal hydroxides and provides multi-component metal hydroxides with increased productivity because it is capable of minimizing discharge or disposal of intermediate reactants due to the saturation of the reactor.

Now, the present invention will be described in more detail with reference to the following examples. These examples should not be construed as limiting the scope of the present invention.

Nickel sulfate, cobalt sulfate and manganese sulfate were mixed in a molar ratio of 80:10:10 and mixed with water subjected to reverse osmosis (RO water) to prepare a metal salt solution having a concentration of 2.0M.

In the preparation device as shown in, 200 L of RO water was fed into a 500 L reactor, the temperature was set to 60° C., and nitrogen gas was fed at a flow rate of 0.5 L/min for 30 minutes or more to create an inert atmosphere. 1 L of 25% NaOH and 5 L of 25% aqueous ammonia were fed to the reactor to adjust the NHconcentration to 6,000 ppm or more and the pH to 12.0 or more, the metal salt solution was fed at about 0.3 to 0.5 L/min through the upper nozzle of the reactor, while stirring at a rate of 320 rpm, and co-precipitation was initiated.

When co-precipitation was continuously performed in the reactor, the initial NHconcentration and the pH were gradually changed. 25% aqueous ammonia was added to maintain the NHconcentration at 3,500 to 5,000 ppm, and an aqueous 25% NaOH solution was added thereto to maintain the pH at 11.5 to 12.2.